1. Field of the Invention
The invention relates to a new process for preparing imidazopyridine derivatives of the general formula: ##STR4## wherein R.sub.1 is an alkyl, cycloalkyl, aryl or aralkyl group or is a heterocyclic radical, R.sub.2 and R.sub.4 are identical or different and are hydrogen, a hydroxy, a cyano, alkyl, cycloalkyl, aryl or aralkyl group or are an alkanoyl or an alkoxy-carbonyl group, and R.sub.3 is hydrogen, an alkyl, aryl or aralkyl group or a halogen atom.
2. Background Art
The literature reference J. Med. Chem., (1991), 34, 2919-2922, describes how the above-described imidazopyridines can be obtained by reduction of 2-amino-3-nitropyridines and by subsequent condensation with an appropriate aliphatic carboxylic acid. However, the preparation of the starting materials for the 2-amino-3-nitropyridines is difficult, since the nitration of the corresponding aminopyridines does not proceed regioselectively.